package style.zcyLeetCode.a_0005_二叉树;

/**
 * 找到后继节点
 *
 * 1、x节点有右树的时候，后继节点就是右树的最左节点
 * 2、x节点无右树的时候，往上走（判断是不是父亲的左孩子，是 即是后继节点）
 * 3、总有一个节点的后继是null
 */
public class SuccessorNode {
    public static class Node {
        public int value;
        public Node left;
        public Node right;
        public Node parent;
        public Node (int data) {
            this.value = data;
        }
    }
    
    public static Node getSuccessorNode(Node node) {
        if (node == null) {
            return node;
        }

        if (node.right != null) {
            // 有右树
            return getLeftMost(node.right);
        } else {
            // 无右树
            Node parent = node.parent;
            // parent == null 整棵树最右的节点
            // 当前节点是其父亲节点的右孩子
            while (parent != null && parent.left != node) {
                // node、parent都往上移动
                node = parent;
                parent = node.parent;
            }
            return parent;
        }
    }

    // 获取节点最左树
    public static Node getLeftMost(Node node) {
        if (node == null) {
            return node;
        }
        while (node.left != null) {
            node = node.left;
        }
        return node;
    }

    public static void main(String[] args) {
        Node head = new Node(6);
        head.parent = null;
        head.left = new Node(3);
        head.left.parent = head;
        head.left.left = new Node(1);
        head.left.left.parent = head.left;
        head.left.left.right = new Node(2);
        head.left.left.right.parent = head.left.left;
        head.left.right = new Node(4);
        head.left.right.parent = head.left;
        head.left.right.right = new Node(5);
        head.left.right.right.parent = head.left.right;
        head.right = new Node(9);
        head.right.parent = head;
        head.right.left = new Node(8);
        head.right.left.parent = head.right;
        head.right.left.left = new Node(7);
        head.right.left.left.parent = head.right.left;
        head.right.right = new Node(10);
        head.right.right.parent = head.right;

        Node test = head.left.left;
        System.out.println(test.value + " next: " + getSuccessorNode(test).value);
        test = head.left.left.right;
        System.out.println(test.value + " next: " + getSuccessorNode(test).value);
        test = head.left;
        System.out.println(test.value + " next: " + getSuccessorNode(test).value);
        test = head.left.right;
        System.out.println(test.value + " next: " + getSuccessorNode(test).value);
        test = head.left.right.right;
        System.out.println(test.value + " next: " + getSuccessorNode(test).value);
        test = head;
        System.out.println(test.value + " next: " + getSuccessorNode(test).value);
        test = head.right.left.left;
        System.out.println(test.value + " next: " + getSuccessorNode(test).value);
        test = head.right.left;
        System.out.println(test.value + " next: " + getSuccessorNode(test).value);
        test = head.right;
        System.out.println(test.value + " next: " + getSuccessorNode(test).value);
        test = head.right.right; // 10's next is null
        System.out.println(test.value + " next: " + getSuccessorNode(test));
    }
}
